/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.util;

import java.util.Map.Entry;

/**
 * This class provides a skeletal implementation of the <tt>Map</tt>
 * interface, to minimize the effort required to implement this interface.
 *
 * <p>To implement an unmodifiable map, the programmer needs only to extend this
 * class and provide an implementation for the <tt>entrySet</tt> method, which
 * returns a set-view of the map's mappings.  Typically, the returned set
 * will, in turn, be implemented atop <tt>AbstractSet</tt>.  This set should
 * not support the <tt>add</tt> or <tt>remove</tt> methods, and its iterator
 * should not support the <tt>remove</tt> method.
 *
 * <p>To implement a modifiable map, the programmer must additionally override
 * this class's <tt>put</tt> method (which otherwise throws an
 * <tt>UnsupportedOperationException</tt>), and the iterator returned by
 * <tt>entrySet().iterator()</tt> must additionally implement its
 * <tt>remove</tt> method.
 *
 * <p>The programmer should generally provide a void (no argument) and map
 * constructor, as per the recommendation in the <tt>Map</tt> interface
 * specification.
 *
 * <p>The documentation for each non-abstract method in this class describes its
 * implementation in detail.  Each of these methods may be overridden if the
 * map being implemented admits a more efficient implementation.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <K> the type of keys maintained by this map
 * @param <V> the type of mapped values
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Map
 * @see Collection
 * @since 1.2
 */

public abstract class AbstractMap<K, V> implements Map<K, V> {

  /**
   * Sole constructor.  (For invocation by subclass constructors, typically
   * implicit.)
   */
  protected AbstractMap() {
  }

  // Query Operations

  /**
   * {@inheritDoc}
   *
   * @implSpec This implementation returns <tt>entrySet().size()</tt>.
   */
  public int size() {
    return entrySet().size();
  }

  /**
   * {@inheritDoc}
   *
   * @implSpec This implementation returns <tt>size() == 0</tt>.
   */
  public boolean isEmpty() {
    return size() == 0;
  }

  /**
   * {@inheritDoc}
   *
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @implSpec This implementation iterates over <tt>entrySet()</tt> searching for an entry with the
   * specified value.  If such an entry is found, <tt>true</tt> is returned.  If the iteration
   * terminates without finding such an entry, <tt>false</tt> is returned.  Note that this
   * implementation requires linear time in the size of the map.
   */
  public boolean containsValue(Object value) {
    Iterator<Entry<K, V>> i = entrySet().iterator();
    if (value == null) {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (e.getValue() == null) {
          return true;
        }
      }
    } else {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (value.equals(e.getValue())) {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * {@inheritDoc}
   *
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @implSpec This implementation iterates over <tt>entrySet()</tt> searching for an entry with the
   * specified key.  If such an entry is found, <tt>true</tt> is returned.  If the iteration
   * terminates without finding such an entry, <tt>false</tt> is returned.  Note that this
   * implementation requires linear time in the size of the map; many implementations will override
   * this method.
   */
  public boolean containsKey(Object key) {
    Iterator<Map.Entry<K, V>> i = entrySet().iterator();
    if (key == null) {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (e.getKey() == null) {
          return true;
        }
      }
    } else {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (key.equals(e.getKey())) {
          return true;
        }
      }
    }
    return false;
  }

  /**
   * {@inheritDoc}
   *
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @implSpec This implementation iterates over <tt>entrySet()</tt> searching for an entry with the
   * specified key.  If such an entry is found, the entry's value is returned.  If the iteration
   * terminates without finding such an entry, <tt>null</tt> is returned.  Note that this
   * implementation requires linear time in the size of the map; many implementations will override
   * this method.
   */
  public V get(Object key) {
    Iterator<Entry<K, V>> i = entrySet().iterator();
    if (key == null) {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (e.getKey() == null) {
          return e.getValue();
        }
      }
    } else {
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        if (key.equals(e.getKey())) {
          return e.getValue();
        }
      }
    }
    return null;
  }

  // Modification Operations

  /**
   * {@inheritDoc}
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @throws IllegalArgumentException {@inheritDoc}
   * @implSpec This implementation always throws an <tt>UnsupportedOperationException</tt>.
   */
  public V put(K key, V value) {
    throw new UnsupportedOperationException();
  }

  /**
   * {@inheritDoc}
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @implSpec This implementation iterates over <tt>entrySet()</tt> searching for an entry with the
   * specified key.  If such an entry is found, its value is obtained with its <tt>getValue</tt>
   * operation, the entry is removed from the collection (and the backing map) with the iterator's
   * <tt>remove</tt> operation, and the saved value is returned.  If the iteration terminates
   * without finding such an entry, <tt>null</tt> is returned.  Note that this implementation
   * requires linear time in the size of the map; many implementations will override this method.
   *
   * <p>Note that this implementation throws an <tt>UnsupportedOperationException</tt> if the
   * <tt>entrySet</tt> iterator does not support the <tt>remove</tt> method and this map contains a
   * mapping for the specified key.
   */
  public V remove(Object key) {
    Iterator<Entry<K, V>> i = entrySet().iterator();
    Entry<K, V> correctEntry = null;
    if (key == null) {
      while (correctEntry == null && i.hasNext()) {
        Entry<K, V> e = i.next();
        if (e.getKey() == null) {
          correctEntry = e;
        }
      }
    } else {
      while (correctEntry == null && i.hasNext()) {
        Entry<K, V> e = i.next();
        if (key.equals(e.getKey())) {
          correctEntry = e;
        }
      }
    }

    V oldValue = null;
    if (correctEntry != null) {
      oldValue = correctEntry.getValue();
      i.remove();
    }
    return oldValue;
  }

  // Bulk Operations

  /**
   * {@inheritDoc}
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @throws IllegalArgumentException {@inheritDoc}
   * @implSpec This implementation iterates over the specified map's <tt>entrySet()</tt> collection,
   * and calls this map's <tt>put</tt> operation once for each entry returned by the iteration.
   *
   * <p>Note that this implementation throws an <tt>UnsupportedOperationException</tt> if this map
   * does not support the <tt>put</tt> operation and the specified map is nonempty.
   */
  public void putAll(Map<? extends K, ? extends V> m) {
    for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
      put(e.getKey(), e.getValue());
    }
  }

  /**
   * {@inheritDoc}
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @implSpec This implementation calls <tt>entrySet().clear()</tt>.
   *
   * <p>Note that this implementation throws an <tt>UnsupportedOperationException</tt> if the
   * <tt>entrySet</tt> does not support the <tt>clear</tt> operation.
   */
  public void clear() {
    entrySet().clear();
  }

  // Views

  /**
   * Each of these fields are initialized to contain an instance of the
   * appropriate view the first time this view is requested.  The views are
   * stateless, so there's no reason to create more than one of each.
   */
  transient volatile Set<K> keySet;
  transient volatile Collection<V> values;

  /**
   * {@inheritDoc}
   *
   * @implSpec This implementation returns a set that subclasses {@link AbstractSet}. The subclass's
   * iterator method returns a "wrapper object" over this map's <tt>entrySet()</tt> iterator.  The
   * <tt>size</tt> method delegates to this map's <tt>size</tt> method and the <tt>contains</tt>
   * method delegates to this map's <tt>containsKey</tt> method.
   *
   * <p>The set is created the first time this method is called, and returned in response to all
   * subsequent calls.  No synchronization is performed, so there is a slight chance that multiple
   * calls to this method will not all return the same set.
   */
  public Set<K> keySet() {
    if (keySet == null) {
      keySet = new AbstractSet<K>() {
        public Iterator<K> iterator() {
          return new Iterator<K>() {
            private Iterator<Entry<K, V>> i = entrySet().iterator();

            public boolean hasNext() {
              return i.hasNext();
            }

            public K next() {
              return i.next().getKey();
            }

            public void remove() {
              i.remove();
            }
          };
        }

        public int size() {
          return AbstractMap.this.size();
        }

        public boolean isEmpty() {
          return AbstractMap.this.isEmpty();
        }

        public void clear() {
          AbstractMap.this.clear();
        }

        public boolean contains(Object k) {
          return AbstractMap.this.containsKey(k);
        }
      };
    }
    return keySet;
  }

  /**
   * {@inheritDoc}
   *
   * @implSpec This implementation returns a collection that subclasses {@link AbstractCollection}.
   * The subclass's iterator method returns a "wrapper object" over this map's <tt>entrySet()</tt>
   * iterator. The <tt>size</tt> method delegates to this map's <tt>size</tt> method and the
   * <tt>contains</tt> method delegates to this map's <tt>containsValue</tt> method.
   *
   * <p>The collection is created the first time this method is called, and returned in response to
   * all subsequent calls.  No synchronization is performed, so there is a slight chance that
   * multiple calls to this method will not all return the same collection.
   */
  public Collection<V> values() {
    if (values == null) {
      values = new AbstractCollection<V>() {
        public Iterator<V> iterator() {
          return new Iterator<V>() {
            private Iterator<Entry<K, V>> i = entrySet().iterator();

            public boolean hasNext() {
              return i.hasNext();
            }

            public V next() {
              return i.next().getValue();
            }

            public void remove() {
              i.remove();
            }
          };
        }

        public int size() {
          return AbstractMap.this.size();
        }

        public boolean isEmpty() {
          return AbstractMap.this.isEmpty();
        }

        public void clear() {
          AbstractMap.this.clear();
        }

        public boolean contains(Object v) {
          return AbstractMap.this.containsValue(v);
        }
      };
    }
    return values;
  }

  public abstract Set<Entry<K, V>> entrySet();

  // Comparison and hashing

  /**
   * Compares the specified object with this map for equality.  Returns
   * <tt>true</tt> if the given object is also a map and the two maps
   * represent the same mappings.  More formally, two maps <tt>m1</tt> and
   * <tt>m2</tt> represent the same mappings if
   * <tt>m1.entrySet().equals(m2.entrySet())</tt>.  This ensures that the
   * <tt>equals</tt> method works properly across different implementations
   * of the <tt>Map</tt> interface.
   *
   * @param o object to be compared for equality with this map
   * @return <tt>true</tt> if the specified object is equal to this map
   * @implSpec This implementation first checks if the specified object is this map; if so it
   * returns <tt>true</tt>.  Then, it checks if the specified object is a map whose size is
   * identical to the size of this map; if not, it returns <tt>false</tt>.  If so, it iterates over
   * this map's <tt>entrySet</tt> collection, and checks that the specified map contains each
   * mapping that this map contains.  If the specified map fails to contain such a mapping,
   * <tt>false</tt> is returned.  If the iteration completes, <tt>true</tt> is returned.
   */
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    }

    if (!(o instanceof Map)) {
      return false;
    }
    Map<?, ?> m = (Map<?, ?>) o;
    if (m.size() != size()) {
      return false;
    }

    try {
      Iterator<Entry<K, V>> i = entrySet().iterator();
      while (i.hasNext()) {
        Entry<K, V> e = i.next();
        K key = e.getKey();
        V value = e.getValue();
        if (value == null) {
          if (!(m.get(key) == null && m.containsKey(key))) {
            return false;
          }
        } else {
          if (!value.equals(m.get(key))) {
            return false;
          }
        }
      }
    } catch (ClassCastException unused) {
      return false;
    } catch (NullPointerException unused) {
      return false;
    }

    return true;
  }

  /**
   * Returns the hash code value for this map.  The hash code of a map is
   * defined to be the sum of the hash codes of each entry in the map's
   * <tt>entrySet()</tt> view.  This ensures that <tt>m1.equals(m2)</tt>
   * implies that <tt>m1.hashCode()==m2.hashCode()</tt> for any two maps
   * <tt>m1</tt> and <tt>m2</tt>, as required by the general contract of
   * {@link Object#hashCode}.
   *
   * @return the hash code value for this map
   * @implSpec This implementation iterates over <tt>entrySet()</tt>, calling {@link
   * Map.Entry#hashCode hashCode()} on each element (entry) in the set, and adding up the results.
   * @see Map.Entry#hashCode()
   * @see Object#equals(Object)
   * @see Set#equals(Object)
   */
  public int hashCode() {
    int h = 0;
    Iterator<Entry<K, V>> i = entrySet().iterator();
    while (i.hasNext()) {
      h += i.next().hashCode();
    }
    return h;
  }

  /**
   * Returns a string representation of this map.  The string representation
   * consists of a list of key-value mappings in the order returned by the
   * map's <tt>entrySet</tt> view's iterator, enclosed in braces
   * (<tt>"{}"</tt>).  Adjacent mappings are separated by the characters
   * <tt>", "</tt> (comma and space).  Each key-value mapping is rendered as
   * the key followed by an equals sign (<tt>"="</tt>) followed by the
   * associated value.  Keys and values are converted to strings as by
   * {@link String#valueOf(Object)}.
   *
   * @return a string representation of this map
   */
  public String toString() {
    Iterator<Entry<K, V>> i = entrySet().iterator();
    if (!i.hasNext()) {
      return "{}";
    }

    StringBuilder sb = new StringBuilder();
    sb.append('{');
    for (; ; ) {
      Entry<K, V> e = i.next();
      K key = e.getKey();
      V value = e.getValue();
      sb.append(key == this ? "(this Map)" : key);
      sb.append('=');
      sb.append(value == this ? "(this Map)" : value);
      if (!i.hasNext()) {
        return sb.append('}').toString();
      }
      sb.append(',').append(' ');
    }
  }

  /**
   * Returns a shallow copy of this <tt>AbstractMap</tt> instance: the keys
   * and values themselves are not cloned.
   *
   * @return a shallow copy of this map
   */
  protected Object clone() throws CloneNotSupportedException {
    AbstractMap<?, ?> result = (AbstractMap<?, ?>) super.clone();
    result.keySet = null;
    result.values = null;
    return result;
  }

  /**
   * Utility method for SimpleEntry and SimpleImmutableEntry.
   * Test for equality, checking for nulls.
   *
   * NB: Do not replace with Object.equals until JDK-8015417 is resolved.
   */
  private static boolean eq(Object o1, Object o2) {
    return o1 == null ? o2 == null : o1.equals(o2);
  }

  // Implementation Note: SimpleEntry and SimpleImmutableEntry
  // are distinct unrelated classes, even though they share
  // some code. Since you can't add or subtract final-ness
  // of a field in a subclass, they can't share representations,
  // and the amount of duplicated code is too small to warrant
  // exposing a common abstract class.


  /**
   * An Entry maintaining a key and a value.  The value may be
   * changed using the <tt>setValue</tt> method.  This class
   * facilitates the process of building custom map
   * implementations. For example, it may be convenient to return
   * arrays of <tt>SimpleEntry</tt> instances in method
   * <tt>Map.entrySet().toArray</tt>.
   *
   * @since 1.6
   */
  public static class SimpleEntry<K, V>
      implements Entry<K, V>, java.io.Serializable {

    private static final long serialVersionUID = -8499721149061103585L;

    private final K key;
    private V value;

    /**
     * Creates an entry representing a mapping from the specified
     * key to the specified value.
     *
     * @param key the key represented by this entry
     * @param value the value represented by this entry
     */
    public SimpleEntry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    /**
     * Creates an entry representing the same mapping as the
     * specified entry.
     *
     * @param entry the entry to copy
     */
    public SimpleEntry(Entry<? extends K, ? extends V> entry) {
      this.key = entry.getKey();
      this.value = entry.getValue();
    }

    /**
     * Returns the key corresponding to this entry.
     *
     * @return the key corresponding to this entry
     */
    public K getKey() {
      return key;
    }

    /**
     * Returns the value corresponding to this entry.
     *
     * @return the value corresponding to this entry
     */
    public V getValue() {
      return value;
    }

    /**
     * Replaces the value corresponding to this entry with the specified
     * value.
     *
     * @param value new value to be stored in this entry
     * @return the old value corresponding to the entry
     */
    public V setValue(V value) {
      V oldValue = this.value;
      this.value = value;
      return oldValue;
    }

    /**
     * Compares the specified object with this entry for equality.
     * Returns {@code true} if the given object is also a map entry and
     * the two entries represent the same mapping.  More formally, two
     * entries {@code e1} and {@code e2} represent the same mapping
     * if<pre>
     *   (e1.getKey()==null ?
     *    e2.getKey()==null :
     *    e1.getKey().equals(e2.getKey()))
     *   &amp;&amp;
     *   (e1.getValue()==null ?
     *    e2.getValue()==null :
     *    e1.getValue().equals(e2.getValue()))</pre>
     * This ensures that the {@code equals} method works properly across
     * different implementations of the {@code Map.Entry} interface.
     *
     * @param o object to be compared for equality with this map entry
     * @return {@code true} if the specified object is equal to this map entry
     * @see #hashCode
     */
    public boolean equals(Object o) {
      if (!(o instanceof Map.Entry)) {
        return false;
      }
      Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
      return eq(key, e.getKey()) && eq(value, e.getValue());
    }

    /**
     * Returns the hash code value for this map entry.  The hash code
     * of a map entry {@code e} is defined to be: <pre>
     *   (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
     *   (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
     * This ensures that {@code e1.equals(e2)} implies that
     * {@code e1.hashCode()==e2.hashCode()} for any two Entries
     * {@code e1} and {@code e2}, as required by the general
     * contract of {@link Object#hashCode}.
     *
     * @return the hash code value for this map entry
     * @see #equals
     */
    public int hashCode() {
      return (key == null ? 0 : key.hashCode()) ^
          (value == null ? 0 : value.hashCode());
    }

    /**
     * Returns a String representation of this map entry.  This
     * implementation returns the string representation of this
     * entry's key followed by the equals character ("<tt>=</tt>")
     * followed by the string representation of this entry's value.
     *
     * @return a String representation of this map entry
     */
    public String toString() {
      return key + "=" + value;
    }

  }

  /**
   * An Entry maintaining an immutable key and value.  This class
   * does not support method <tt>setValue</tt>.  This class may be
   * convenient in methods that return thread-safe snapshots of
   * key-value mappings.
   *
   * @since 1.6
   */
  public static class SimpleImmutableEntry<K, V>
      implements Entry<K, V>, java.io.Serializable {

    private static final long serialVersionUID = 7138329143949025153L;

    private final K key;
    private final V value;

    /**
     * Creates an entry representing a mapping from the specified
     * key to the specified value.
     *
     * @param key the key represented by this entry
     * @param value the value represented by this entry
     */
    public SimpleImmutableEntry(K key, V value) {
      this.key = key;
      this.value = value;
    }

    /**
     * Creates an entry representing the same mapping as the
     * specified entry.
     *
     * @param entry the entry to copy
     */
    public SimpleImmutableEntry(Entry<? extends K, ? extends V> entry) {
      this.key = entry.getKey();
      this.value = entry.getValue();
    }

    /**
     * Returns the key corresponding to this entry.
     *
     * @return the key corresponding to this entry
     */
    public K getKey() {
      return key;
    }

    /**
     * Returns the value corresponding to this entry.
     *
     * @return the value corresponding to this entry
     */
    public V getValue() {
      return value;
    }

    /**
     * Replaces the value corresponding to this entry with the specified
     * value (optional operation).  This implementation simply throws
     * <tt>UnsupportedOperationException</tt>, as this class implements
     * an <i>immutable</i> map entry.
     *
     * @param value new value to be stored in this entry
     * @return (Does not return)
     * @throws UnsupportedOperationException always
     */
    public V setValue(V value) {
      throw new UnsupportedOperationException();
    }

    /**
     * Compares the specified object with this entry for equality.
     * Returns {@code true} if the given object is also a map entry and
     * the two entries represent the same mapping.  More formally, two
     * entries {@code e1} and {@code e2} represent the same mapping
     * if<pre>
     *   (e1.getKey()==null ?
     *    e2.getKey()==null :
     *    e1.getKey().equals(e2.getKey()))
     *   &amp;&amp;
     *   (e1.getValue()==null ?
     *    e2.getValue()==null :
     *    e1.getValue().equals(e2.getValue()))</pre>
     * This ensures that the {@code equals} method works properly across
     * different implementations of the {@code Map.Entry} interface.
     *
     * @param o object to be compared for equality with this map entry
     * @return {@code true} if the specified object is equal to this map entry
     * @see #hashCode
     */
    public boolean equals(Object o) {
      if (!(o instanceof Map.Entry)) {
        return false;
      }
      Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
      return eq(key, e.getKey()) && eq(value, e.getValue());
    }

    /**
     * Returns the hash code value for this map entry.  The hash code
     * of a map entry {@code e} is defined to be: <pre>
     *   (e.getKey()==null   ? 0 : e.getKey().hashCode()) ^
     *   (e.getValue()==null ? 0 : e.getValue().hashCode())</pre>
     * This ensures that {@code e1.equals(e2)} implies that
     * {@code e1.hashCode()==e2.hashCode()} for any two Entries
     * {@code e1} and {@code e2}, as required by the general
     * contract of {@link Object#hashCode}.
     *
     * @return the hash code value for this map entry
     * @see #equals
     */
    public int hashCode() {
      return (key == null ? 0 : key.hashCode()) ^
          (value == null ? 0 : value.hashCode());
    }

    /**
     * Returns a String representation of this map entry.  This
     * implementation returns the string representation of this
     * entry's key followed by the equals character ("<tt>=</tt>")
     * followed by the string representation of this entry's value.
     *
     * @return a String representation of this map entry
     */
    public String toString() {
      return key + "=" + value;
    }

  }

}
